EPROM memories with floating grill are programmable electrically, but are not erasable electrically. These memories are erasable only by ultraviolet rays. EPROM memories are programmed by using the phenomenon of thermal agitation in the conduction channel under the effect of conventional saturation. This phenomenon is irreversible.
EEPROM memories are programmable and erasable electrically. EEPROM memories are programmed or erased via tunnel effect. Internal memory circuits, such as charge pumps or multipliers, usually produce programming and erasing voltages.
Flash memories are components formed by a matrix of memory cells, each having a transistor with floating gate. In conventional terms, it is possible to individually each program each cell of the matrix, but the data must be erased for a block of cells. Each cell is usually formed from a source, a drain, a floating gate and a control cell. The transistors with floating gate of the matrix are arranged in rows. Forming a source line connects the sources of the transistors of a row. Hot carriers of the drain program the cell. The cell is erased by tunnel effect.
The production process for certain flash memories utilises an etching step known as forming an auto-aligned or SAS source (Self-Aligned Source). The SAS etching digs out source lines in the substrate on which the flash memory is formed. During a subsequent stage of the process arsenic is implanted at a high concentration in the etched zone to form the source line of the transistors with floating gate.
Although useful, Flash memories have disadvantages. One disadvantage is the time required to erase flash memories is considerable, thus limiting their fields of application.
Accordingly, a need exists to overcome these disadvantages with process for a Flash memory.